This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Fluid therapy is important, especially in very sick patients, and also important for the replacement of fluids and other elements lost during surgery. Previous sheep studies have shown that anesthesia gases promote the accumulation of fluid outside of blood vessels. Furthermore, in sheep models, anesthesia gases have been shown to blunt the refilling response that capillaries normally have to fluid loss. The goal of this project is to determine if anesthesia gases decrease the production of urine and cause fluid to be allocated outside the blood vessels in human participants during a controlled bleed. To accomplish these goals, we will enroll 12 volunteers into our fluid kinetics study. Body fluid shifts will be calculated using a commonly used method known as the indicator dilution technique to asses the baseline volume status. After the baseline is measured, hemoglobin values will be collected at regular intervals. Each participant will take part in 4 arms of the study over a period of six months. The description of the 4 arms of the study is as follows: 1. conscious, blood withdrawal, no fluid infusion (awake only) 2. anesthetized, blood withdrawal, no fluid infusion (asleep only) 3. conscious, blood withdrawal, fluid infusion (awake plus infusion) 4. anesthetized, blood withdrawal, fluid infusion (asleep plus infusion) The importance of this study is the ability to better manage a common clinical occurrence.